One of the achievements in Assassin’s Creed 2 is to collect all 100 feathers. I would venture to say that this is nearly impossible without the use of guide maps. Just some of the feathers are in extremely hard to find spots that you wouldn’t consider checking. When you collect all 100 feathers you will be rewarded with the Auditore cape – It gives you full notoriety in every city except your own town.

There are plenty of guides online to help you find the feathers. I think Games Radar has a great guide for locating all 100 feathers.
View the guide here.